This invention relates to single cell and multi-cell regenerative photovoltaic photoelectrochemical (RPEC) devices, and to materials and methods used for manufacture of such devices.
Examples of the RPEC cells of the type concerned are disclosed in the following U.S. patents.
U.S. Pat. No. 4,927,721, Photoelectrochemical cell; Michael Graetzel and Paul Liska, 1990.
U.S. Pat. No. 5,350,644, Photovoltaic cells: Michael Graetzel, Mohammad K Nazeeruddin and Brian O""Regan, 1994.
U.S. Pat. No. 5,525,440, Method of manufacture of photo-electrochemical cell and a cell made by this method; Andreas Kay, Michael Graetzel and Brian O""Regan, 1996.
U.S. Pat. No. 5,728,487, Photoelectrochemical cell and electrolyte for this cell; Michael GraetzeL Yordan Athanassov and Pierre Bonhote, 1998.
RPEC cells, as of the type disclosed in the above patents, are capable of being fabricated in a laminate arrangement between two large area substrates without undue expense. One typical arrangement involves two glass substrates, each utilising an electrically conducting coating upon the internal surface of the substrate. Another typical arrangement involves the first substrate being glass or polymeric and utilising an electrically conducting coating upon the internal surface of the substrate, with the second substrate being polymeric. In some arrangements, the internal surface of said second polymeric substrate is coated with an electrically conducting coating, whereas in other arrangements, said second polymeric substrate comprises a polymeric foil laminate, utilising adjacent electrically conductive material, such as carbon. Also, in some arrangements, the external surface may be a laminated metal film, and in other arrangements, the external surface may be coated by a metal. At least one of said first and second substrates is substantially transparent to visible light, as in the attached transparent electrically conducting (TEC) coating. RPEC cells contain a photoanode, typically comprising a ruthenium dye-sensitised, nanoporous semiconducting oxide (eg. titania) layer attached to one conductive coating, and a cathode, typically comprising a redox electrocatalyst layer attached to the other conductive coating or conductive material. An electrolyte containing a redox mediator is located between the photoanode and cathode, and the electrolyte is sealed from the environment. If one or more polymer substrates are utilised, the photoanode and the cathode are typically electrically separated by a porous insulating layer (eg. insulating ceramic oxides) or spacer(s) (eg. insulating spheres). TEC coatings, which usually comprise a metal oxide(s), have high resistivity when compared with normal metal conductors, resulting in high resistive losses for large area RPEC cells operating under high illumination. When operating under high illumination, one method to minimise these losses is the deposition of one or more networks of electrically conductive material that serve to collect and/or distribute electrons in the cell. Another method to minimise these losses is by connecting a multiple of RPEC cells (here called xe2x80x98RPEC modulesxe2x80x99) in series to generate higher voltages and to minimise total current. Such connections in RPEC modules may be made externally or internally (International Application PCT/AU00/00190). To enable internal series connection of adjacent RPEC cells, selected areas of such conducting coatings must be electrically isolated, portions of such areas overlapped when laminated, interconnects used to connect such overlapped areas and electrolyte-impermeable barriers used to separate the electrolyte of individual cells.
One example of the manufacture of an RPEC module involves the use of two glass substrates that have TEC-coatings that have been divided into electrically isolated regions. Titanium dioxide (or similar semiconductor) is screen printed onto selected areas of the TEC coating of one substrate and an electrocatalyst is screen printed onto selected areas of the TEC coating of the other substrate. The titanium dioxide (titania) is coated with a thin layer of a dye by immersion of the titania-coated substrate in the dye solution. Strips of sealant and interconnect material are deposited upon one of the substrates and the two substrates are then bonded together. Electrolyte is added to the cells via access apertures in one of the substrates and these apertures are then sealed.
Another example of the manufacture of an RPEC module involves the use of one substrate with a TEC-coating that has been divided into electrically isolated regions. Successive layers of titania, insulating ceramic oxide, and conducting catalytic material (for example, carbon-based) are deposited, for example by screen printing, onto selected areas of the TEC-coated substrate, with the catalytic layer also serving as an interconnect. The titania is coated with a thin layer of the dye by immersion of the multiple-coated substrate in the dye solution. Electrolyte is added to the spaces within the porous titania-insulator-catalytic layers. The sealant face of a sealant/polymer and/or metal foil laminate is sealed to the substrate.
One of the difficulties in the manufacture of RPEC cells and modules is that when the semiconducting oxide-coated substrate is exposed to the dye solution, dye not only adsorbs to the semiconducting oxide, but also to the conductive coating. Similarly, if sealant has been applied to the semiconducting oxide-coated substrate, exposure to the dye solution typically results in dye adsorption to the sealant surface. The adsorbed dye on the conductive coating or sealant can interfere with the strength and/or permeability of any bond made to these surfaces during sealing, and also can affect the performance and service life of the RPEC cell. One process that prevents dye adsorption to the conductive coating involves covering relevant areas of the conducting coating with a polymeric film, application of dye to the coated substrate and then removal of the polymeric film, thus leaving a clean conductive coating surface to which a subsequent seal may be made. Another process that prevents dye adsorption to the conductive coating involves use of a laminated film (eg. surlyn/polypropylene) in which one face (eg. the surlyn face) is sealed to the relevant areas of the conducting coating, after which the dye is applied to the coated substrate and then the upper layer (eg. polypropylene) is removed, thus leaving a clean polymer (eg. surlyn) surface to which a subsequent seal may be made. This subsequent seal may involve additional sealant material or may involve-sealing directly to the sealant surface, with the seal being made to a coated glass substrate or to a polymeric foil laminate, such as surlyn/aluminium. Unfortunately, these protective film processes are inconvenient and time consuming and can result in variability in performance of the RPEC. An additional impediment to a continuous manufacturing process is that dye application to the semiconducting oxide needs to be automated to be carried out efficiently, preferably within a low volume container that may be dark, heated, and provided with a partially sealed, low-oxygen content atmosphere.
The present invention provides a method for manufacturing regenerative photoelectrochemical (RPEC) devices in a production line, each device being deposited on a substrate, the method comprising the steps of:
attaching at least one substrate to the protective film in such a way that a predetermined areas of the substrate are protected from being coated during at least one subsequent manufacturing process;
The protective film may comprise a patterned composite, laminated or multilayer film (CLM film) and the substrate may be a multiply-coated substrate of RPEC cells and modules. The protective film may be patterned to create apertures, which are used as engagement means and the step of transporting the substrate comprises penetrating the engagement means with teeth to locate and mechanically engage the film in transportation of the film/substrate composite.
The method allows continuous and convenient transport of the CLM film/substrate composite, using the engagement means, through one or more steps of the manufacturing process, including, but not limited to application of dye to the semiconductor oxide, addition of electrolyte, continuous removal of part of said patterned CLM film and sealing of the multiply-coated substrate to another substrate. The patterned film has the advantage of preventing adsorption of dye on the predetermined areas of said substrate. A portion of the part of said patterned film not removed may be utilised as sealant to subsequently bond the substrates of the RPEC cells and modules.
In one embodiment, the present invention provides for application of a continuous patterned CLM film to a multiply-coated substrate of RPEC cells and modules, and continuous and convenient transport of the patterned film/substrate composite through one or more steps of the manufacturing process, including, but not limited to application of dye to the semiconductor oxide, addition of electrolyte, continuous removal of part of said patterned CLM film and scaling of the multiply-coated substrate to another substrate.
The patterned film may be a laminate of two or more polymers plus the option of an external layer of metallic or other materials, whereby one of the external layers of the laminate will function as the sealant of the RPEC device. The other layer(s) of the laminate function to prevent access of the dye, electrolyte, solvents and/or other materials to one face of the sealant layer. The patterned film may be dispensed in a substantially continuous sheet, preferably from a roll, and may be continuously patterned using stamping, rolling or any of the known methods of such patterning, to remove portions of film, thereby leaving apertures, hereby termed access regions, and optionally also leaving other apertures, hereby termed engagement means. If desired, a sealant face of said patterned film and/or predetermined areas of the surface of the multiply-coated substrate are treated with an adhesion promoting means, such as an adhesion primer, corona discharge or other known processes, in order to effect superior adhesion of said treated face and/or said treated surface in the subsequent bonding process, The substrate may be bonded to said patterned film by using roller, hot roller, stamping, or hot stamping processes, or by any of the known methods of such bonding. Particular care must be taken in the bonding process to ensure desired alignment of multiply-coated areas of said substrates with said access regions of said patterned film. Said access regions enable access to at least one selected area of said substrate, by dye solutions, electrolyte, solvents, gases and such like materials in subsequent steps of said continuous manufacturing process. Mechanical contact is made with said patterned film in order to transport said patterned film attached to the substrate i.e. the xe2x80x9cfilm/substrate compositexe2x80x9d, through subsequent steps of said continuous manufacturing process. Said mechanical contact may comprise any of the known methods of mechanical contact used to transport a film. Said mechanical contact includes, but is not limited to penetration of said engagement means by projections that are then moved to effect said transport, whereby said projections include, but are not limited to teeth of sprockets, teeth in linear placement as in racks, hooks supports and such like mechanical devices as are known to those of ordinary skill in the art. Said sprockets may be round, or essentially triangular, square, polygonal or of any suitable shape, and the apertures comprising the engagement means may be square, round or of any suitable shape, and may form one or more lines along the length of said patterned film. Said mechanical contact may include, but is not limited to opposing sets of rollers touching said film that passes between said sets of rollers, and with first set of rollers moved in opposite rotation to second set of rollers in order to transport said film in the desired direction. Said patterned film/substrate composite may be transported through a dye application chamber that may be dark, heated, and provided with a partially sealed, low-oxygen content atmosphere. Within said dye application chamber, said patterned film/substrate composite may be transported through the dye solution in a zig-zag manner, linearly, or in any other manner to provide effective use of the solution and space. Said dye solution may be agitated, such as by bubbles, stirring, pumping, ultrasonics or other known means of agitation. Said patterned film/substrate composite may be transported through a rinsing chamber, an electrolyte chamber, and other chambers, including but not limited to drying chambers. Part of said patterned film may then be removed in a continuous process, leaving the sealant layer of the patterned film adhering to regions of said multiply-coated substrate. Said mechanical contact with said sealant layer film enables convenient transport of said sealant film/substrate composite through subsequent steps of said continuous manufacturing process, including sealing of exposed surface of clean sealant on said multiply-coated substrate to a second substrate. Said multiply-coated substrate may comprise a TEC-coated glass substrate or a polymeric substrate, upon which subsequent layers of material are deposited. Said second substrate may comprise a TEC-coated glass substrate, a polymeric substrate, or a polymeric/metal foil laminate, such as surlyn/aluminium, whereby part of the polymeric layer (eg. surlyn) of said polymeric/metal foil laminate (eg. surlyn/aluminium) is bonded to said remaining patterned polymeric film (eg. surlyn) that is adhering to regions of the multiply-coated substrate. If used, polymeric substrates and polymeric/metal foil laminates, may be dispensed in a substantially continuous sheet, preferably from a roll.
Throughout this specification, unless the context requires otherwise, the word xe2x80x9ccomprisexe2x80x9d or variations such as xe2x80x9ccomprisesxe2x80x9d or xe2x80x9ccomprisingxe2x80x9d, will be understood to imply the inclusion of a stated element or integer or group of elements or integers but not the exclusion of any other element or integer or group of elements or integers.